No tickets (or ANYTHING, really) are ever "added to" any MagicBand.
Just to keep things as clear as possible-
There is no reservation info, or ticket info, or credit card info, or FP+ info "put onto" a MagicBand.
A MagicBand only contains a unique serial number that is used to access the information that is stored in a guest's MyDisneyExperience file.
When the MagicBand is touched to a "Mickey Head Reader,"
the MB's serial number is read and that number creates a an instant connection to the the guest's
MDE account info.
The MagicBand works like the combination to a locked safe, or a key to a locked door.
The MB, itself, is not the container of the ticket or FastPass, or Room key number, etc.
The MB just
unlocks the guest's file of info, allowing it to be accessed from her/his MDX account when needed.
So... WHENEVER you get new tickets or add a day or change to AP, etc.
the change will be made in your MDX account and any MB you have will be able to access
that change, immediately.